1. Field of the Invention
This invention is in the field of internal combustion engines and in particular pistons for such engines.
2. Discussion of Related Technology
A piston arrangement for achieving improved control over ignition and combustion characteristics of a fuel charge in an internal combustion engine and a process for achieving such controlled ignition and combustion by the generation and management of fuel radical species within the combustion chamber of such an engine is described in U.S. Pat. No. 4,898,135 granted Feb. 6, 1990. In accordance with the patent, a piston for an internal combustion engine, which may be spark or compression ignited, includes a central recess for receiving the majority of each charge during each combustion cycle of the engine and a reaction chamber adjacent the recess for receiving a portion of the fuel and air of each charge. During each combustion cycle, the portion of the charge that is disposed in the reaction chamber undergoes a cool flame oxidation reaction to produce fuel radical species that are discharged in a next succeeding combustion cycle for seeding the next charge admitted to the combustion chamber.
In accordance with the teachings of the aforesaid patent, the generation and management of fuel radical species requires control over the manner in which the fuel and air of each charge is admitted into the reaction chamber and also the manner in which outgasing of the reaction chamber into the combustion zone occurs. In accordance with the prior patent, a continuous slot orifice having critical dimensions is provided to primarily receive fuel and air into the reaction chamber under choked flow conditions during the compression event of each combustion cycle and to enable outgasing of the chamber into the main combustion chamber also under choked flow conditions, whereby a supply of fuel radical species is 15 preserved during each combustion cycle for use in the next combustion cycle due to the time delay in outgasing of the reaction chamber. Optionally, in accordance with the teachings of the prior patent, one or more discrete orifices may also be provided to provide communication between the piston recess and the reaction chamber to achieve better control over the admission of fuel to the reaction chamber.
For a complete discussion of the benefits provided by the piston configuration described in the prior patent, and for a more complete explanation of the manner in which fuel radical species are generated and managed in accordance with a piston having a configuration as described above, reference may be had to the written description and drawings of the prior patent. Essentially, the patent describes the manner in which controlled seeding of a fuel charge before ignition in an internal combustion engine can be utilized to produce dependable and predictable ignition and knock-free combustion of fuels that otherwise would be considered difficult to ignite without ignition improvers or subject to knock during certain engine operating conditions, depending upon the type of engine utilized. In accordance with the prior patent, the generation and management of the supply of radicals in the combustion chamber to achieve the recognized benefits of seeding a fuel charge with such radicals involves using a reaction chamber located adjacent a piston recess with a system that provides controlled communication between the main combustion chamber of the engine and the reaction chamber.
While the use of an appropriately dimensioned continuous slot orifice was considered to be an appropriate means for achieving controlled communication between the main combustion chamber and the reaction chamber in accordance with the prior patent, it has more recently been discovered that the continuous slot orifice can present heat transfer problems in the crown region of the piston and moreover creates certain difficulties in enabling the control of air and fuel admitted to the reaction chamber. It has been observed that it would be highly desirable to more closely control the admission of air and fuel components into the reaction chamber and to enable better heat transfer between the crown portion of the piston and the main body of the piston in the area that previously was dedicated to the continuous slot orifice.